Population cycles are characteristic of small mammals, and they sometimes appear to be brought about by predators.
数量的周期循环是小型哺乳动物的特征，它们有时似乎是由捕食者造成的。
2
Considering human capital as a characteristic of the population, however, all four countries were advantaged by the large percentages of their populations who could read and write.
但是，考虑到人力资本是人口的一个特点，这四个国家都因其具有读写能力的人口占比大而更有优势。
3
A defining characteristic of a pandemic is the almost universal vulnerability of the world's population to infection. Not all people become infected, but nearly all people are at risk.